The identification of period-doubling in a nonlinear two-degree-of-freedom electromagnetic vibrational energy harvester

Common vibrational energy harvesters are generally based on a linear mass-spring oscillator model, and these typically show narrow bandwidth and high resonant frequency at small scales. To overcome these problems, a two-degree-of-freedom nonlinear velocity-amplified energy harvester has been developed. The device comprises two masses, relatively oscillating one inside the other between four sets of magnetic springs. The magnetic springs introduce nonlinear effects, such as period doubling, that can be exploited to enhance the output power and bandwidth of the harvester. This article studies the dynamics of the harvester when a key geometrical parameter (the height of the device) is varied. For large height values, a significant increase of the output power in regions far from the resonant frequency of the device is observed, and the associated period-doubling effect was verified through high-speed imaging. It is demonstrated that nonlinear effects can be used to enhance the bandwidth of the device in order to harvest energy in regions far from resonance.